As a rule, NFL defensive linemen don't tolerate slaps to the face or getting their hair pulled.

Steelers defensive end Brett Keisel makes a notable exception. It is for his son, Jacob, who has possibly made him a better football player and has definitely made him a more dedicated one.

"Brett used to be a guy that would come in before meetings and then lift," Steelers defensive end Aaron Smith said. "Now, he's in here first thing in the morning, getting his stuff done."

Keisel and left tackle Marvel Smith became first-time fathers during the offseason -- their sons were born approximately two months apart -- and each said the experience has changed their perspective and given them even more purpose on the playing field.

"It made me realize how important my job is, to not only myself but to my family," said Keisel, who turns 30 a week from Thursday. "It just made me work that much harder to be that much better of a player."

The change Aaron Smith has seen in Keisel does not surprise him.

He went through a similar transformation after he and his wife started their family.

"I always tell people this, but someone told me a long time ago 'If you're not motivated when you have your first child, you'll never be motivated in your life,' " said Smith, whose wife gave birth to the couple's fourth child in June.

Neither Keisel nor Marvel Smith appeared to be lacking for motivation in the Steelers' 38-17 win over the Houston Texans on Sunday.

Keisel was part of a front seven that harassed Matt Schaub into two interceptions and sacked the Texans quarterback five times. Smith, meanwhile, got the better of Houston defensive end Mario Williams, one of the premier pass rushers in the NFL.

Williams twice sacked Steelers quarterback Ben Roethlisberger, but the Texans' defensive line was not much of a factor. Roethlisberger had twice as many touchdown passes (two) as incompletions (one), and Willie Parker rushed for 138 yards and a career-high three touchdowns.

Smith, who turned 30, has said the back surgery he had last December rejuvenated him and added years to his career.

When it comes to the most significant development in his life in the last year, however, it's not even close. The birth of his son, Kingston, trumps everything.

"I don't care about nothing but him really," Smith said. "My whole career I've been playing for myself. Now, since I've got a little boy it's like trying to make sure everything is right for him down the road."

Juggling football with fatherhood can be tricky, and there is an adjustment period.

"You've got kids waking up at 2, 3 in the morning like everyone else in this world, but a lack of sleep in this business is hard because your body needs to recover," Aaron Smith said. "It definitely takes a while to get used to having children and playing."

Marvel Smith wouldn't have it any other way.

The same goes for Keisel.

"It's such a miracle," he said. "To watch him grow and watch him progress, he's starting to slap me on the face and grab my beard and pull my hair. It's just so cool because it's kind of like looking at yourself a little bit."